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  1. JDK
  2. JDK-8259021

SharedSecrets should avoid double racy reads from non-volatile fields

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 17
    • Component/s: client-libs
    • Labels:
      None
    • Resolved In Build:
      b04

      Description

      Some XxxAccess instances in jdk.internal.access.SharedSecrets are initialized lazily on 1st access with the following idiom:

          public static JavaUtilJarAccess javaUtilJarAccess() {
              if (javaUtilJarAccess == null) {
                  // Ensure JarFile is initialized; we know that this class
                  // provides the shared secret
                  ensureClassInitialized(JarFile.class);
              }
              return javaUtilJarAccess;
          }

      But this idiom is flawed in concurrent setting. It may happen that the two reads of javaUtilJarAccess non-volatile field get reordered and so the 1st read (in if condition) reads non-null while the 2nd read (in return) reads null. This can be fixed by introducing a local variable that avoids the 2nd read:

          public static JavaUtilJarAccess javaUtilJarAccess() {
              var access = javaUtilJarAccess;
              if (access == null) {
                  // Ensure JarFile is initialized; we know that this class
                  // provides the shared secret
                  ensureClassInitialized(JarFile.class);
                  access = javaUtilJarAccess;
              }
              return access;
          }

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              Assignee:
              plevart Peter Levart
              Reporter:
              plevart Peter Levart
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                Created:
                Updated:
                Resolved: